The year was 1374. In dozens of medieval towns scattered along the valley of the River Rhine hundreds of people were seized by an agonising compulsion to dance. Scarcely pausing to rest or eat, they danced for hours or even days in succession. They were victims of one of the strangest afflictions in Western history. Within weeks the mania had engulfed large areas of north-eastern France and the Netherlands, and only after several months did the epidemic subside. In the following century there were only a few isolated outbreaks of compulsive dancing. Then it reappeared, explosively, in the city of Strasbourg in 1518. Chronicles indicate that it then consumed about 400 men, women and children, causing dozens of deaths (Waller, 2008).
Not long before the Strasbourg dancing epidemic, an equally strange compulsion had gripped a nunnery in the Spanish Netherlands. In 1491 several nuns were ‘possessed’ by devilish familiars which impelled them to race around like dogs, jump out of trees in imitation of birds or miaow and claw their way up tree trunks in the manner of cats. Such possession epidemics were by no means confined to nunneries, but nuns were disproportionately affected (Newman, 1998). Over the next 200 years, in nunneries everywhere from Rome to Paris, hundreds were plunged into states of frantic delirium during which they foamed, screamed and convulsed, sexually propositioned exorcists and priests, and confessed to having carnal relations with devils or Christ.The article examines these phenomena, dismissing various theories (such as them being caused by ergotism, or the consumption of bread contaminated with hallucinogenic mould), and makes the case that they were culture-bound psychogenic illnesses, enabled by accepted beliefs about the supernatural and triggered by stress:
Similarly, it is only by taking cultural context seriously that we can explain the striking epidemiological facts that possession crises so often struck religious houses and that men were far less often the victims of mass diabolical possession. The daily lives of nuns were saturated in a mystical supernaturalism, their imaginations vivid with devils, demons, Satanic familiars and wrathful saints. They believed implicitly in the possibility of possession and so made themselves susceptible to it. Evangelical Mother Superiors often made them more vulnerable by encouraging trance and ecstasy; mind-altering forms of worship prepared them for later entering involuntary possession states. Moreover, early modern women were imbued with the idea that as the tainted heirs of Eve they were more liable to succumb to Satan, a misogynistic trope that often heightened their suggestibility.
Theological conventions also conditioned the behaviour of demoniac nuns. This is apparent from the fact that nearly all possession epidemics occurred within a single 300-year period, from around 1400 to the early 1700s. The reason is that only during this period did religious writers insist that such events were possible (Newman 1998). Theologians, inquisitors and exorcists established the rules of mass demonic possession to which dissociating nuns then unconsciously conformed: writhing, foaming, convulsing, dancing, laughing, speaking in tongues and making obscene gestures and propositions. These were shocking but entirely stereotypical performances based on deep-seated beliefs about Satan’s depravity drawn from religious writings and from accounts of previous possessions. For centuries, then, distress and pious fear worked in concert to produce epidemics of dancing and possession.The article concludes with examples of modern occurrences of such phenomena, from the rather feeble examples (such as epidemics of fainting) one could find in a materialistic post-Enlightenment society to "spirit possession" among factory workers drawn from rural communities in Malaysia and Singapore, to delusions of penis-stealing witchcraft in western Africa.
Here's what I find interesting about delusions: Like all animals, humans have a nervous system that is designed to input information from the environment and thereby form beliefs that are true and relevant to the nervous system's owner. This is pretty much all a nervous systems has to do. There must be enormous selection pressure for it to work properly. Imagine if an animal was not aware of food, predators, mates etc, or had an incorrect view of their importance. Yet humans seem to be capable of no end of delusions. (Apart from the examples above, see Taleb's book "Fooled by Randomness" and numerous others.) So we have a contradiction: on the one hand we seem to be a very successful species; on the other hand one of our key pieces of adaptive equipment doesn't seem to work, a lot of the time. If this line of reasoning leads to a contradiction, it must contain a false premise or deduction. So, what is wrong with it?
Humans also have complex culture. I suspect that humans have delusions and dogs and horses don't for the same reason why PCs are susceptible to viruses and toasters aren't.
How do you know dogs and horses don't have delusions?
That's a good point Andrew, but are you just shifting the paradox? We have complex culture because our minds enable it. We shouldn't evolve a feature that enables unadaptive behaviour. I guess either the pros of gullibility/culture outweigh the cons, or there is an arms race between spreaders and receivers of delusions.
Well, culture (i.e., memes) can evolve orders of magnitude faster than biology can, and can adapt to changing environments. As long as the failure cases aren't immediately catastrophic, the competition doesn't stand a chance.
It is indeed possible that dogs and horses can experience delusions, though without language, culture and social institutions, they would presumably not grow into the elaborate cultural phenomena human delusions do.
Another way to ask my question is: why doesn't a mutant human, less vulnerable to memes/culture and therefore mass delusions, evolve to out-compete we culture-vultures? In a way the answer is obvious: the pros of being culture-enabled must outweigh the cons. Still, it's interesting to ponder the detailed pros and cons. Perhaps when humans have all gone up in smoke, post-nuclear/environmental catastrophe, our successors will look back at us and say (would they have language?) "They were too easily manipulable by each other".
Well, look at the non-linguistic competition. They're stuck in trees, hunting with sticks and picking lice off each other's pelts for want of smalltalk. Perhaps evolution could, eventually, produce creatures hardwired for more advanced social organisation without culture, but that would also mean not having technology. And they would still suffer the disadvantage of not having the flexibility of cultural, rather than genetic, adaptation.
Take me to the disco. Everybody dance, it's the end of the world.
Turn off that fan, it's stealing my oxygen.